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This is an early access version, the complete PDF, HTML, and XML versions will be available soon.
Article

Thermally Stable and Energy Efficient Newly Synthesized Bipolar Emitters for Yellow and Green OLED Devices

by
Anil Kumar
1,
Sushanta Lenka
1,
Kapil Patidar
1,
Chih-An Tung
1,
Ming Yu Luo
1,
Raminta Beresneviciute
2,
Gintare Krucaite
2,
Daiva Tavgeniene
2,
Dovydas Blazevicius
2,
Bernadeta Blazeviciute
2,
Jwo-Huei Jou
1,* and
Saulius Grigalevicius
2,*
1
Department of Materials Science and Engineering, National Tsing Hua University, No. 101, Section 2, Guangfu Rd., East District, Hsinchu 30013, Taiwan
2
Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu Plentas 19, LT50254 Kaunas, Lithuania
*
Authors to whom correspondence should be addressed.
Molecules 2026, 31(1), 158; https://doi.org/10.3390/molecules31010158 (registering DOI)
Submission received: 17 November 2025 / Revised: 11 December 2025 / Accepted: 22 December 2025 / Published: 1 January 2026
(This article belongs to the Topic Materials, Structure Designs and Device Fabrications for Highly Efficient/Long Lifetime Organic Light-Emitting Diodes)
Versions Notes

Abstract

Organic light-emitting diodes (OLEDs) have emerged as a leading high-resolution display and lighting technology, as well as for photo-therapeutic applications, due to their light weight, flexibility, and excellent color rendering. However, achieving long-term thermal stability and high energy efficiency remains a principal issue for their widespread adoption. Strong thermal robustness in OLED emitter materials is a critical parameter for achieving long device lifetimes, stable film morphology, reliable high-temperature processing, and sustained interface integrity in high-performance hosts. Bipolar emitters RB14 (N-(9-ethylcarbazole-3-yl)-4-(diphenylamino)phenyl-9H-carbazole-9-yl-1,8-naphthalimide), RB18 (N-phenyl-4-(diphenylamino)phenyl-9H-carbazole-9-yl-1,8-naphthalimide), and RB22 (N-phenyl-3-(2-methoxypyridin-3-yl)-9H-carbazole-9-yl-1,8-naphthalimide) were newly synthesized. RB18 is a yellow bipolar OLED emitter that has a glass transition temperature (Tg) of 162 °C and thermal durability (Td) of 431 °C, which is the highest reported value for naphthalimide-based bipolar emitter derivatives for yellow OLEDs. Meanwhile, RB14 and RB22 are green OLED emitters that have glass transition temperatures (Tg) of 133 °C and 167 °C, and thermal durabilities (Td) of 336 °C and 400 °C, respectively. We have fabricated OLED devices using these bipolar emitters dispersed in CBP host matrix, and we have found that the maximum EQEs (%) for RB14, RB18, and RB22 emitter-based devices are 7.93%, 3.40%, and 4.02%, respectively. For confirmation of thermal stability, we also used UV-visible spectroscopy measurements at variable temperatures on annealed spin-coated glass films of these emitter materials and found that RB22 is the most thermally stable emitter among these materials.
Keywords: bipolar emitter; thermal stability; glass transition temperature; organic light-emitting diode; efficiency; photo-therapeutic bipolar emitter; thermal stability; glass transition temperature; organic light-emitting diode; efficiency; photo-therapeutic

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MDPI and ACS Style

Kumar, A.; Lenka, S.; Patidar, K.; Tung, C.-A.; Luo, M.Y.; Beresneviciute, R.; Krucaite, G.; Tavgeniene, D.; Blazevicius, D.; Blazeviciute, B.; et al. Thermally Stable and Energy Efficient Newly Synthesized Bipolar Emitters for Yellow and Green OLED Devices. Molecules 2026, 31, 158. https://doi.org/10.3390/molecules31010158

AMA Style

Kumar A, Lenka S, Patidar K, Tung C-A, Luo MY, Beresneviciute R, Krucaite G, Tavgeniene D, Blazevicius D, Blazeviciute B, et al. Thermally Stable and Energy Efficient Newly Synthesized Bipolar Emitters for Yellow and Green OLED Devices. Molecules. 2026; 31(1):158. https://doi.org/10.3390/molecules31010158

Chicago/Turabian Style

Kumar, Anil, Sushanta Lenka, Kapil Patidar, Chih-An Tung, Ming Yu Luo, Raminta Beresneviciute, Gintare Krucaite, Daiva Tavgeniene, Dovydas Blazevicius, Bernadeta Blazeviciute, and et al. 2026. "Thermally Stable and Energy Efficient Newly Synthesized Bipolar Emitters for Yellow and Green OLED Devices" Molecules 31, no. 1: 158. https://doi.org/10.3390/molecules31010158

APA Style

Kumar, A., Lenka, S., Patidar, K., Tung, C.-A., Luo, M. Y., Beresneviciute, R., Krucaite, G., Tavgeniene, D., Blazevicius, D., Blazeviciute, B., Jou, J.-H., & Grigalevicius, S. (2026). Thermally Stable and Energy Efficient Newly Synthesized Bipolar Emitters for Yellow and Green OLED Devices. Molecules, 31(1), 158. https://doi.org/10.3390/molecules31010158

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